Using simulated galaxies in their cosmological context, we analyse how the flaring of mono-age populations (MAPs) influences the flaring and the age structure of geometrically-defined thick discs. We also explore under which circumstances the geometric thin and thick discs are meaningfully distinct components, or are part of a single continuous structure as in the Milky Way. We find that flat thick discs are created when MAPs barely flare or have low surface density at the radius where they start flaring. When looking at the vertical distribution of MAPs, these galaxies show a continuous thin/thick structure. They also have radial age gradients and tend to have quiescent merger histories. Those characteristics are consistent with what is observed in the Milky Way. Flared thick discs, on the other hand, are created when the MAPs that flare have a high surface density at the radius where they start flaring. The thick discs' scale-heights can either be dominated by multiple MAPs or just a few, depending on the mass and scale-height distribution of the MAPs. In a large fraction of these galaxies, thin and thick discs are clearly distinct structures. Finally, flared thick discs have diverse radial age gradients and merger histories, with galaxies that are more massive or that have undergone massive mergers showing flatter age radial gradients in their thick disc.

中文翻译：

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关于星系厚盘的爆发：来自模拟的见解

在其宇宙学背景下使用模拟星系，我们分析了单一年龄群体 (MAP) 的爆发如何影响几何定义的厚圆盘的爆发和年龄结构。我们还探讨了在什么情况下几何薄圆盘和厚圆盘是有意义的不同组件，或者是银河系中单个连续结构的一部分。我们发现，当 MAP 几乎不张开或在它们开始张开的半径处具有低表面密度时，就会产生扁平厚圆盘。当观察 MAP 的垂直分布时，这些星系显示出连续的薄/厚结构。它们还具有径向年龄梯度，并且往往具有静止的合并历史。这些特征与在银河系中观察到的一致。另一方面，张开的厚圆盘，当耀斑的 MAP 在它们开始耀斑的半径处具有高表面密度时，就会产生这种情况。厚圆盘的尺度高度可以由多个 MAP 支配，也可以仅由几个支配，这取决于 MAP 的质量和尺度高度分布。在这些星系的大部分中，薄盘和厚盘是明显不同的结构。最后，张开的厚盘具有不同的径向年龄梯度和合并历史，质量更大或经历过大规模合并的星系在其厚盘中显示出更平坦的年龄径向梯度。薄盘和厚盘是明显不同的结构。最后，张开的厚盘具有不同的径向年龄梯度和合并历史，质量更大或经历过大规模合并的星系在其厚盘中显示出更平坦的年龄径向梯度。薄盘和厚盘是明显不同的结构。最后，张开的厚盘具有不同的径向年龄梯度和合并历史，质量更大或经历过大规模合并的星系在其厚盘中显示出更平坦的年龄径向梯度。